1. Field of the Invention
The present invention relates to an electronic unit casing in which an electronic unit such as a power conversion device is housed.
2. Related Art
An electronic unit such as a power conversion device, which includes a power module with a high heat output value, is often housed in a casing cooled with a cooling device so as to improve the heat radiating effect. Japanese Laid-Open Patent Publication No. 2003-69270 discloses a cooling casing that adopts an electromagnetic wave shielding structure in order to reduce the leakage of electromagnetic waves generated in the power conversion device and the entry of external electromagnetic waves.
In the casing in the related art described above the electronic unit is disposed on a base member cooled with a cooling device, with a metal lid secured with bolts atop a side wall disposed so as to surround the electronic unit. A seal member such as an O-ring seal is disposed over tightening surfaces of the lid and the side wall at which they are fastened to each other, and thus, the casing is waterproofed. The side wall is formed by using a member having a double-layer structure constituted with a resin and a metal plate in order to minimize the weight of the casing and reduce the extent of heat entering from the external environment where the temperature may be very high.
The metal plate constituting the side wall, which is included in order to assure satisfactory levels of cooling performance and electromagnetic wave shielding performance, is partially exposed at the tightening surface of the side wall, and the exposed metal plate is placed in contact with the metal lid. As a result, the electromagnetic wave shielding performance in the casing is assured and, at the same time, the electronic unit housed inside the casing is expected to be cooled with better efficiency.
However, since the O-ring seal is disposed between the exposed portion of the metal plate and the bolt tightening portions, the lid may be allowed to tilt at the O-ring seal forming a fulcrum when the bolts are being tightened to lead to incomplete contact between the lid and the exposed metal plate portion or even to a complete failure to achieve contact due to a gap formed between them. In such an event, the electromagnetic wave shielding performance and the cooling performance would become poor.